Paramagnetic gas components can be analyzed in different ways in gap(s) of one or more magnets while using variable magnetic field(s) for instance. One such alternative is disclosed in the patent publication U.S. Pat. No. 6,430,987 describing an apparatus for measuring the proportion of a paramagnetic gas in a gas sample. For the purpose the apparatus comprises: a first modulatable magnetic field source with a first air gap; a second modulatable magnetic field source with a second air gap; a modulation source for outputting a modulation signal to the magnetic field sources; a reversing switch means, which connects the modulation source to the first magnetic field source and the second magnetic field source in alternation; a measuring element, located in the air gaps, for outputting a heat flow measurement signal, which measuring element comprises a thermocouple arrangement with at least one first connection point and one second connection point, the thermocouple arrangement being positioned such that the first connection point is located in the first air gap and the second connection point is located in the second air gap; an alternating current source, connected to the thermocouple arrangement, by which source the thermocouple arrangement is heated to an operating temperature that is elevated compared to the gas sample; a filter device, connected to the thermocouple arrangement, for filtering out periodic fluctuations from the heat flow measurement signal caused by the modulation of the magnetic field sources, the amplitude of the periodic fluctuations being a measure for the proportion of the paramagnetic gas in the gas sample. Accordingly, here the proportion of a paramagnetic gas component is analyzed with thermocouple(s) having at least two sensing points in two gaps of magnets to detect a change of thermal conductivity, but without a reference gas, i.e. only sample gas is fed in to the gaps. Other than paramagnetic gas components cannot be measured with this system.
Another alternative is to use e.g. a microphone to detect the pressure difference between the sample gas and the reference gas fed into one air gap of a magnet. For this purpose the patent publication U.S. Pat. No. 4,633,705 discloses a measuring cell for measuring the oxygen content of a gas mixture comprising: a member having a closed cavity therein; a sample gas conduit extending into said cavity for supplying sample gas to said measuring cell; a reference gas conduit extending into said cavity for supplying reference gas to said measuring cell; an exit conduit for removing gases from said cavity; an electromagnet positioned in said cavity, said electromagnet having a core with spaced opposing magnetic poles forming an air gap therebetween, said electromagnet being energizable by chopped direct current for establishing a magnetic field in said air gap, at least one of said magnetic poles having passages extending therethrough and opening into said air gap, said passages being connected to said gas conduits for supplying sample and reference gases to said gap; and pedestals mounted in said air gap adjacent the openings of said passages for guiding the gases for mixing in said air gap, said mixed gases being discharged into said cavity for removal via said exit conduit. Accordingly, this publication discloses the basic concept for analyzing the content of a paramagnetic gas component in a gas mixture utilizing the paramagnetic susceptibility. Patent publication U.S. Pat. No. 4,808,921 also describes an apparatus for determining the concentration of a paramagnetic gas by measuring its pressure when subjected to an AC magnetic field. Here the apparatus comprises an AC electromagnet with an almost closed ferromagnetic circuit, a permanent magnet and a gap, a chamber positioned within said gap inlet and outlet lines for the gas to be analyzed as well as a gas of known magnetic susceptibility and means for measuring differential gas pressures in the respective lines created when the gas to be analyzed and the gas of known magnetic susceptibility are subjected to a combined AC and DC magnetic field generated by the electromagnet having an AC current winding and the permanent magnet wherein the DC magnetic field is superimposed onto the AC magnetic field by the permanent magnet. According to this publication, the magnetic powers generate the stray field and vibrations that influences the microphones via their nickel membranes, which causes generation of a false signal at a frequency of 2ω, i.e. twice the measuring frequency, which false signals do not influence the measuring signal at the one measuring frequency ω. These two publications disclose quite analogous ways for analyzing a paramagnetic gas component, like oxygen.
Non-paramagnetic gas components in a gas mixture are typically analyzed by measuring the optical absorption—dispersively or non-dispersively—they cause in a beam of radiation, which radiation can be visible light, but in most cases infrared radiation, or by measuring the amount of radiation, e.g. intensity of light, emitted from a chemiluminescent reaction between certain gas components. Of course wavelengths practical or available for the purpose are used. These optical analyzing methods are useful as such, but analyzing both paramagnetic and non-paramagnetic gas components from the same gas mixture requires complicated system, i.e. at least two different analyzers, one for the paramagnetic gas(es) and another for the non-paramagnetic gas(es).